A disproportionate thickened ventricular septum is a relatively common finding (prevalence about 25%) in infants with a variety of congenital heart diseases. Such abnormal septal-free wall ratios are probably a function of small differences between septal and free thicknesses in hearts with relatively thin ventricular walls. An abnormal septal-free wall ratio cannot be used as the sole criterion for identifying hypertropic cardiomyopathy in infants with other heart diseases.